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Patients are more likely to suffer from vitamin B-12 deficiency than the reverse, MedlinePlus claims. Excess vitamin B-12 is often removed in the urine and does not pose a problem for patients. Doctors do not generally use a vitamin B-12 blood test to find high levels of the substance. People who do have consistently high levels of the vitamin may have a serious condition. In rare cases, diabetics and obese people may have high levels of the vitamin, WebMD says.